Top 12 America's Youngest Billionaires

The Facebook phenomenon strikes again, this time helping catapult two new 20-somethings into the ranks of America's richest for the first time and bringing down the average age of America's richest ever so slightly to 65.7. Only eight American billionaires are under the age of 40, and three of them co-founded Facebook.

The youngest? It isn't who you think it is. The world's youngest billionaire is now 26-year-old Dustin Moskovitz, who is eight days younger than his former Harvard roommate and Facebook co-founder Mark Zuckerberg. The social-networking site's first chief technology officer, Moskovitz left in 2008 and started Asana, a software company that allows individuals and small companies to better collaborate. The company has attracted several of the same early backers as Facebook and may one day be worth something.Moskovitz's entire $1.4 billion fortune comes from his 6 percent stake in Facebook.

Zuckerberg may no longer reign as the youngest member of the Forbes 400, but he has bragging rights as the year's biggest percentage gainer -- his net worth jumped to $6.9 billion, up from $2 billion, making him worth nearly five times as much as Moskovitz and more than even Apple's (Nasdaq: AAPL - News) Steve Jobs.

The third Facebook co-founder among the ranks is 28-year-old Eduardo Saverin, who once owned a one-third stake in Facebook. When Zuckerberg and Moskovitz quit school to relocate to California, Saverin stayed behind to graduate. A year later Facebook sued him; he countersued. The parties settled with Saverin apparently getting a 5 percent stake and a co-founder bio on Facebook's site. Don't feel bad. We estimate that share makes him worth $1.15 billion.

Technology, and in particular the Internet, has long been the best bet for getting rich at a young age. Bill Gates made his debut on the list in 1986 at age 30 with a net worth of $315 million. Michael Dell debuted at age 26; 19 years later, he is still among the list's 20 youngest. So too for Yahoo's (Nasdaq: YHOO - News) David Filo and Jerry Yang, who first made the ranks a dozen years ago. Indeed half of the 20 youngest America billionaires have made their fortunes in the tech industry, most via the Internet.

Outside the world of the Internet, young rich-list members have been able to cash in from a few other industries such as finance and sports. Hedge fund manager John Arnold, 36, got his start as an oil trader for Enron in 1995. He is said to have earned $750 million for the company in 2001. When Enron collapsed a year later, he went into business for himself, founding Centaurus, a hedge fund focusing mostly on natural gas, energy trading.

Five of the 20 youngest inherited their fortunes, including Scott Duncan, the only billionaire in his 20s who didn't strike it rich with Facebook. He and his siblings assumed control of the family's $12.4 billion pipeline empire after their father Dan Duncan's death last March.

Worth noting about this bunch is not simply how quickly they've made their money, but how they are choosing to spend it, not so much on luxury homes or expensive toys but on causes about which they are passionate. Google's (Nasdaq: GOOG - News) Larry Page is buying up chunks of residential Palo Alto for a network of houses that use new types of fuel cells, geothermal energy and rainwater capture. He also rides a Zero X electric dirt bike and an electric sports car from Tesla Motors, in which he and Sergey Brin are investors. EBay's (Nasdaq: EBAY - News) Pierre Omidyar has donated to everything from a company that designs solar powered lanters to a political satire show in Kenya. Moskovitz gave $70,000 in support of Proposition 19, which is seeking to legalize marijuana in California in November. John Arnold has agreed to take the 

Giving Pledge, making the commitment to give the majority of his wealth to charity.

As for Zuckerberg, he still lives in a relatively modest rental home in Palo Alto, Calif. So what's he doing with his wealth? Not much so far, given that most of it is tied up in non-public shares of Facebook. Still, the 26-year-old announced on "The Oprah Winfrey Show" in September that he is giving away $100 million to Newark's schools. The gift is the largest philanthropic act by a person his age in American history.

Here's a look at the list:

Dustin Moskovitz

Net Worth: $1.4 billion           
Source: Facebook
Age: 26

America's youngest billionaire is eight days younger than his former Harvard roommate Mark Zuckerberg. Facebook's first chief technology officer, he left in 2008 to start Asana, a software company that allows individuals and small companies to better collaborate. For now, his entire fortune comes from his 6 percent stake in Facebook.

Mark Zuckerberg

                             

Net Worth: $6.9 billion
Source: Facebook
Age: 26

The Harvard dropout and Facebook CEO was the biggest percentage gainer on this year's Forbes 400 list and the unwitting star of box-office hit "The Social Network." Last month he agreed to donate $100 million to Newark's troubled schools.

Scott Duncan

Net Worth: $3.1 billion
Source: pipelines
Age: 27

The son of the late Dan Duncan assumed control of part of his family's $12.4 billion pipeline empire after his father's death last March. Their energy company, Enterprise Products, owns more than 49,000 miles of pipelines.

Eduardo Saverin

        

Net Worth: $1.15 billion
Source: Facebook
Age: 28

Brazilian-born Saverin co-founded Facebook with Harvard classmate Mark Zuckerberg and for a brief time had a one-third stake. When Zuckerberg quit school to relocate to California, Saverin stayed behind to graduate. A year later Facebook sued him; he countersued. The parties settled with Saverin apparently getting a 5 percent stake and co-founder bio on Facebook's site.

John Arnold

Net Worth: $3.3 billion
Source: hedge funds
Age: 36

The former Enron oil trader founded hedge fund Centaurus after the energy outfit famously collapsed. His fund now has $5 billion under management, and he and his wife Laura recently pledged half of their wealth to the Gates-Buffet challenge.

Sergey Brin

Net Worth: $15 billion
Source: Google
Age: 37

Emigrated from Russia at age 6; his mother was a research scientist at NASA. He met Larry Page in computer science Ph.D. program at Stanford and dropped out in 1998 to start Google. Brin now focuses on raising margins with Instant Search and building new businesses in communications, and he invests in space travel initiatives and Parkinson's research on the side

Larry Page

Net Worth: $15 billion
Source: Google
Age: 37

The Google co-founder dropped out of his Stanford Ph.D. program in 1998 to start the search engine. Nowadays his personal passions include buying up chunks of residential Palo Alto for a network of houses that use new types of fuel cells, geothermal energy and rainwater capture. He also rides a Zero X electric dirt bike and an electric sports car from Tesla Motors, in which he and Sergey Brin are investors. Page is a board member of the X Prize Foundation, a nonprofit looking for breakthroughs in genomics, energy and space exploration.

Daniel Ziff

Net Worth: $4 billion
Source: inheritance, hedge funds
Age: 38

The youngest son of the late William Ziff Jr., who built the Ziff-Davis publishing empire (PC Magazine, Car & Driver, Boating) and later sold out. Daniel and his brothers Dirk and Robert inherited their father's fortune, which they have since reinvested in Ziff Brothers Investments. He recently got married.

Lorenzo Fertitta

Net Worth: $1 billion
Source: casinos, Ultimate Fighting Championship
Age: 41

Fertitta returns to billionaire status thanks to growing martial arts league Ultimate Fighting Championship, which he owns with his older brother Frank. Abu Dhabi investment is helping UFC go international. A scuba diver, he swims with sharks -- including tigers and great whites -- for fun.

Jerry Yang

Net Worth: $1.15 billion
Source: Yahoo!
Age: 41

Born in Taiwan, Yang moved to the U.S. at age 10. He created his Web directory in 1994 with partner David Filo when both were Stanford grad students. Yahoo! co-founder made his debut among America's 400 richest at age 29. Still with Yahoo!, but no longer its head honcho. He sits on other boards and makes a number of charitable donations.

Ken griffin: 

 

Net Worth: $2.3 billion

Source: hedge funds

Age: 41

Griffin began investing as a Harvard undergrad after he read a Forbes article about the Home Shopping Network. Nowadays his hedge fund Citadel, which has seen assets drop to $11 billion from $20 billion in recent years, is diversifying; it recently launched new funds in equities and mortgages and is jump-starting an investment banking business.

Peter thiel: 

 

Net Worth: $1.1 billion

Source: Paypal, Facebook

Age: 43

Thiel cofounded PayPal in 1998 and sold it to eBay in 2002 for $1.5 billion, personally netting $60 million from the sale. He then invested $500,000 in Facebook in 2004; this stake now makes up the bulk of his net worth. The former national chess champion co-produced the film Thank You for Smoking.